Microwave Dielectric Properties of Ba ₂ Ca _{1− <i>x</i>} Sr _<i>x</i> WO ₆ Double Perovskites

Ba 2 Ca 1− x Sr x WO 6 ( x =0–1) microwave dielectric ceramics have been prepared using the two‐step solid‐state reaction method. The substitution of Sr 2+ for Sr 2+ can effectively lower the densification temperature of the ceramics from 1500° to 1200°C. Single‐phase ceramics with double perovskite structures were obtained, and structural transitions occurred in Ba 2 Ca 1− x Sr x WO 6 via the phase sequence: cubic→rhombohedral→monoclinic with an increase of x . The microwave dielectric properties of the Ba 2 Ca 1− x Sr x WO 6 ceramics can be effectively tuned by tailoring x . The dielectric constant (ɛ r ) remains almost unvaried, the quality factor ( Q × f ) decreases monotonically, and the temperature coefficient of resonant frequency (τ f ) changes in sign with the increase of x . A good combination of the microwave dielectric properties was obtained for Ba 2 Ca 0.975 Sr 0.025 WO 6 sintered at 1250°C: ɛ r =23.9, Q × f =80 200 GHz, and τ f =+18 ppm/°C.

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